Loans and Leases - Composition of Loan and Lease Portfolio (Details) - USD ($) $ in Millions		Sep. 30, 2021		Dec. 31, 2020		Sep. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 43,631		$ 42,822
Non-Covered Loans, Percentage		100.00%		100.00%
Net deferred loan origination costs		$ 56		$ 62
Allowance for credit losses loans and leases		(200)		(194)		$ (188)	$ (148)
Total loans and leases held for investment, net		43,487		42,690
Loans held for sale	[1]			117
Total loans and leases held for investment and held for sale, net		43,487		42,807
Multi-Family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 32,838		$ 32,236
Non-Covered Loans, Percentage		75.27%		75.28%
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 6,715		$ 6,836
Non-Covered Loans, Percentage		15.39%		15.96%
One-to-Four Family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 170		$ 236
Non-Covered Loans, Percentage		0.39%		0.55%
Acquisition, Development, and Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 198		$ 90
Non-Covered Loans, Percentage		0.45%		0.21%
Mortgage Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans	[2]	$ 39,921		$ 39,398
Non-Covered Loans, Percentage	[2]	91.50%		92.00%
Allowance for credit losses loans and leases		$ (177)		$ (176)		$ (171)	$ (123)
Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans	[4]	$ 3,704	[3]	$ 3,417	[5]
Non-Covered Loans, Percentage	[4]	8.49%		7.98%
Commercial and Industrial | Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 1,936		$ 1,682
Non-Covered Loans, Percentage		4.44%		3.93%
Lease Financing, Unearned Income
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 1,768		$ 1,735
Non-Covered Loans, Percentage		4.05%		4.05%
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 6		$ 7
Non-Covered Loans, Percentage		0.01%		0.02%
Total Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 3,710		$ 3,424
Total Other Loans | Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans	[2]	$ 3,710		$ 3,424
Non-Covered Loans, Percentage	[2]	8.50%		8.00%

[1] Includes deferred loan origination fees of $2 million at December 31, 2020.

[2] Excludes accrued interest receivable of $207 million and $219 million at September 30, 2021 and December 31, 2020, respectively, which is included in other assets in the Consolidated Statements of Condition.

[3] Includes lease financing receivables, all of which were classified as Pass.

[4] Includes specialty finance loans and leases of $3.1 billion and $3.0 billion, respectively, at September 30, 2021 and December 31, 2020, and other C&I loans of $561 million and $393 million, respectively, at September 30, 2021 and December 31, 2020.

[5] Includes lease financing receivables, all of which were classified as Pass.